可溶性盐对土壤pH测定的影响及消除初探
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国家科技支撑计划(2014BAD14B04)、国家自然科学基金项目(41401257)和江苏省自然科学青年基金项目(BK20141054)共同资助


Effect of soluble salts on determination of soil pH and its elimination
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    摘要:

    在我国大量施肥的背景下,最近几十年农田土壤酸化速率加快,尤其是设施栽培体系土壤。在淋洗强度较弱的情况下,土壤可伴随有次生盐渍化现象,而可溶性盐的存在对土壤pH(H2O)(用水浸提土壤测得的pH)的测定有显著影响。由于pH是酸化评估的重要指标之一,有必要深入探究农田土壤常见可溶性盐对pH(H2O)测定的影响。本研究中,为精确评估积盐农田土壤的酸化状况,以潮土、褐土、水稻土和红壤为研究对象,研究了农田土壤尤其是设施土壤中常见六种可溶性盐(Ca(NO3)2、KNO3、MgSO4、K2SO4、CaCl2、KCl)对土壤pH测定的影响;并以硝酸钾为研究对象,对比分析了四种消除可溶性盐对pH(H2O)测定影响的方法,这四种方法分别为:用石灰位代替pH(H2O);用0.01 mol L-1 CaCl2浸提代替水浸提;先用模型计算出盐分对pH(H2O)测定的影响,然后从pH(H2O)中减去;用蒸馏水或50℃的50%酒精溶液将土壤中可溶性盐洗除后风干再测定pH(H2O)。结果表明:10 g kg-1可溶性盐的存在可使土壤pH下降0.09~0.87个单位,可溶性盐浓度及土壤电导率(EC)均与pH、△pH(pH的下降程度)之间具有显著的自然对数相关性。同种土壤,不同盐类对pH测定的影响程度不同,强弱顺序因离子组成和土壤类型而异,总体表现为硝酸盐和氯化物对pH测定的影响高于硫酸盐,氯化钙的影响程度高于钾盐及硝酸钙和硫酸镁,三种钾盐之间差异不明显;同种盐类,四种土壤受盐分影响的程度强弱顺序为:褐土 > 水稻土 > 潮土 > 红壤。四种方法均可以减弱或消除硝酸钾对pH测定的影响,6.9 g kg-1硝酸钾施入土壤中可使土壤pH下降0.24~0.71个单位,消除影响后,硝酸钾仅可使土壤pH下降-0.38~0.19个单位。四种方法的简单有效程度为:石灰位> 0.01 mol L-1CaCl2浸提测定pH > 模型拟合计算> 洗盐处理。消除可溶性盐对pH测定的影响可以使积盐的农田土壤酸化评估更为精确,使土壤酸化风险预测更为准确,有利于制定合理有效的风险应对措施。

    Abstract:

    In China, as a result of excessive application of fertilizers, farmland soil acidification has been accelerated in the recent decades, especially in facilitated cultivation systems, and in places where leaching is weak, secondary soil salinization could be observed. The presence of soluble inorganic salts in the soil has some significant effects on determination of soil pH(H2O) (pH in soil-water suspension). Since pH is one of the most important parameters in evaluating soil acidification, it is necessary to study in depth to explore effects of several common soluble salts on determination of farmland soil pH (H2O). To accurately evaluate soil acidification of cultivated lands under secondary salinization, effects of six kinds of soluble salts (Ca(NO3) 2, KNO3, MgSO4, K2SO4, CaCl2 and KCl) in farmland soils (fluvo-aquic soil, cinnamon soil, paddy soil and red soil), especially in greenhouse soils, on determination of soil pH(H2O) were explored in this study. Besides, comparison was done between four methods in effect of eliminating the effect of soluble salts, with potassium nitrate being the object of the study. The four methods were 1) replacing pH(H2O) with lime potential, 2) using 0.01 mol L-1 CaCl2 instead of de-ionized water in extracting soil, 3) figuring out the effect of the soluble salt on determination of soil pH with a model first and deducting what was figured out from the value of pH(H2O) determined, and 4) leaching out soluble salts from the soil with distilled water or 50℃ 50% ethyl alcohol solution first and then air-drying the soils for determination of soil pH(H2O). Results show that the presence of 10 g soluble salt per kilogram soil may bring down soil pH by 0.09~0.87, and both soil electric conductivity and concentration of soluble salts are significantly related to pH and △pH (extent of the drop in pH) in a natural logarithm manner. The six kinds of soluble salts in the same soil differ quite much in effect on determination of soil pH and the sequence of the salts in terms of intensity of the effect varies with soil type and combination of salt ions in the soil. On the whole, the effects of nitrate and chloride are greater than that of sulfate, and the effect of calcium chloride higher than those of calcium nitrate, magnesium sulfate and three potassium salts. However, there is no significant difference between the three potassium salts. The effect of a kind of salts varies with soil type, and the four types of soils display a descending order of cinnamon soil > paddy soil > fluvo-aquic soil > red soil. All the four methods can be used to reduce or eliminate the effect of KNO3 on determination of soil pH. The presence of 6.9 g of potassium nitrate per kilogram soil lowers soil pH(H2O) by 0.24~0.71, or by -0.38~0.19 when the effect of the soluble salt is taken into account or eliminated. In terms of simplicity and effectiveness of the four methods, they follow an order of Method 1) > Method 2) > Method 3) > Method 4). Apparently, elimination of the effects of soluble salts on determination of soil pH can help improve accuracy of the evaluation and risk assessment of soil acidification in farmlands under secondary salinization, and contribute to formulation of reasonable effective risk controlling measures.

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王嫒华,段增强,董金龙,赵 宇,汤 英,李 汛,沈文忠.可溶性盐对土壤pH测定的影响及消除初探[J].土壤学报,2014,51(6):1298-1308. DOI:10.11766/trxb201312090584 Wang Aihua, Duan Zengqiang, Dong Jinlong, Zhao Yu, Tang Ying, Li Xun, Shen Wenzhong. Effect of soluble salts on determination of soil pH and its elimination[J]. Acta Pedologica Sinica,2014,51(6):1298-1308.

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  • 收稿日期:2013-12-09
  • 最后修改日期:2014-08-21
  • 录用日期:2014-08-22
  • 在线发布日期: 2014-08-26
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